Fly ash results from the burning of fuel. Utilities and industries which burn fuel for energy and power generation are oftentimes required to meet strict emission compliance standards for the discharge of fly ash entrained in flue gases. Most of the fly ash entrained in a typical gas is separated by either a mechanical means, such as a cyclone or a bag filter, or through the use of an electrostatic precipitator (ESP). This invention relates to the modification of fly ash porosity in systems which utilize bag houses to separate fly ash from flue gas streams, thereby reducing the energy required to operate and maintain bag house operations.
The inventor has found that the application of various polymer/nitrate compositions into a fly-ash laden gas stream upstream of a bag house increases fly ash porosity, thereby improving the efficiency of bag house operations used to separate dust (fly ash) from flue gas streams. Thus, fly ash solids which are difficult to collect and separate are made more amenable to collection in the bag house.
Currently, the only technique available to keep bag replacement and power costs to a minimum is to balance filter strength and filter permeability. There are two parameters that affect power consumption: the permeability of the filter material and the permeability of the dust cake collected on it. When the pressure drop across the dust cake and the filter exceeds a designated maximum, the bags are mechanically cleaned either by shaking, reverse air flow or reverse pulse air-flow. High frequency of cleaning increases wear and tear whereas operation at too high a pressure drop increases power costs. Treatment of the fly ash with the compositions of this invention helps reduce the energy required to operate and maintain filter bags used in manufacturing and power generating industries.
Conventional technology is to increase the porosity of fly ash by feeding large levels (e.g., about 25 ppm or more) of sulfur trioxide and ammonia into flue gas streams. This requires handling two hazardous, corrosive and potentially toxic gases to achieve results.
Instead of handling two different chemicals (SO.sub.3 & NH.sub.3), the instant process generally only requires the handling of one product, which is a non-toxic, safe and easy to handle aqueous composition. Another advantage is that the formulations described herein can be applied by using simple and low cost feed systems.
U.S. Pat. No. 4,439,351 to Sinha discloses the use of either cationic or anionic polymers to lower the electrical resistivity of fly ash. Copending application U.S. Ser. No. 531,826 is directed to the use of anionic polymer/ammonium nitrate/sodium nitrate compositions to lower the electrical resistivity of fly ash. Sinha, "A New Chemical Conditioner Together with Good Operations and Maintenance Program Management Helps Meet Emissions Objectives" (February 1986), discloses the use of a polymer/ammonium nitrate solution, commercially available from Calgon as FACT 3000, to treat fly ash. The same author, in "A New Chemical Conditioner Together with a Special Feed System Keep Plants on Emission Compliance at Low Treatment Costs" (March 1988), discloses the use of FACT 5000 to treat fly ash in a coal-fired boiler. FACT 5000 is an anionic polymer/sodium nitrate/ammonium nitrate blend available from Calgon Corporation.
None of these references disclose or suggest the use of the instant compositions to increase the porosity of fly ash.